Dicamba Decisions - 3

Dicamba Tank Mix Options for 2017 Start to Roll In

The two new dicamba herbicides have strict tank mix restrictions, including a ban on ammonium salts. Applicators must consult certain websites to verify that additional herbicides or adjuvants are approved, as well. (DTN photo by Pamela Smith)

ROCKVILLE, Md. (DTN) -- Growers and applicators will need to keep a close eye on two tank mix websites if they are spraying newly labeled dicamba herbicides in 2017.

Both Monsanto's XtendiMax and BASF's Engenia herbicides, designed to be applied over Xtend crops, have websites devoted to approved tank mix ingredients. Adding a chemical or additive that is not on those websites is illegal, experts warn.

For now, the pickings are slim; only Engenia has a handful of adjuvants approved for tank mixing. Both companies told DTN they expect that some herbicides, in particular glyphosate, will be added as a legal tank mix option by the beginning of the 2017 growing season.

A number of other ingredients are off the table permanently, including ammonium salts such as ammonium sulfate (AMS) and urea ammonium nitrate (UAN). The Engenia label also bans the use of adjuvants that would decrease the pH and acidify the spray solution.

WEBSITES AIM TO PREVENT DRIFT

At issue is the possibility that certain tank mix ingredients could increase the risk of the new dicamba herbicides drifting, primarily by created more fine, "driftable" spray droplets, said Chad Asmus, technical marketing manager for BASF.

To evaluate this, the tank mix chemicals are run through a wind tunnel test. That data is then evaluated and -- if it passes the parameters set by EPA -- the ingredient can be added to the list of approved products on the tank mix websites.

Engenia currently has 10 approved products listed, all of them adjuvants. Asmus said he is "hopeful" that growers will also have glyphosate options in hand in 2017, as well as some additional herbicides.

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XtendiMax currently has no approved products listed, but Monsanto Crop Protection Systems Lead Ty Witten told DTN they expect to get a "good mix of tank mix partners" approved this week.

Growers are especially eager for tank mix herbicide options, which are needed in order to use multiple modes of action against herbicide-resistant weeds. Glyphosate tank mixing would be especially valuable to growers using Xtend crops, since that trait also includes glyphosate tolerance. However, "the EPA is taking additional time to review tank mixes and evaluating the potential for herbicide synergy between dicamba and glyphosate," Asmus said. (In the context of herbicides, the term "synergy" refers to when two herbicides behave differently when applied together than when applied alone.)

Insecticides and fungicide tank mix partners appear less likely this growing season, and perhaps not at all. Asmus said BASF is "open to the possibility" of adding insecticides and fungicides to the list of approved tank mix options, but the company is currently focused on getting herbicides and adjuvants approved for 2017.

"Insecticides have unique tip requirements," which could affect the "compatibility with the new technologies' large droplet size," Monsanto's Witten added.

VOLATILITY CONCERNS

Both herbicide labels ban ammonium salts and Engenia's label also bans adjuvants that would acidify the spray solution. These restrictions are related to volatility, or the tendency of a chemical to vaporize and drift off target.

"Ammonium salts have a tendency to break down the long chain of molecules that's been added to the BAPMA salt molecule of dicamba [in Engenia]," said University of Arkansas weed scientist Bob Scott. "So if you add ammonium, you will lose your reduced volatility associated with that BAPMA salt. A similar effect occurs with Vapor Grip and the DGA salts [in XtendiMax]."

Likewise, lowering the pH of the spray solution could affect the volatility of Engenia, Asmus added. "If the solution gets too acidic then the volatility reduction benefits associated with the BAPMA salt will be reduced," he said.

DRIFT REDUCTION AGENTS

Some adjuvants are used as drift reduction agents. Both XtendiMax and Engenia labels note that even if a drift reduction agent product is listed on the approved tank mix websites, applicators still need to check with the manufacturer to ensure that the product works with the spray nozzle and spray pressure.

Asmus said this restriction was written for the use of multiple nozzles with dicamba herbicides. As it stands now, Engenia has only one nozzle permitted -- the Turbo TeeJet Induction Flat Spray Tip (TTI11004) -- and Asmus said Engenia's approved tank mix products have been tested with it.

"Suffice to say, applicators can rest assured that if a product is listed on the [Engenia tank mix] website, it is approved and they can use it with that nozzle [TTI11004]," he said.

However, XtendiMax now has 18 additional nozzles approved for use in 2017, so growers using this herbicide face more nozzle choices. "It is always good practice to refer to the labels of all products being used as well as manufacturer requirements," Witten said.

Scott urged applicators to always err on the side of caution when it comes to reading and following the new dicamba labels. "All eyes are on us," he said. "If we're not able to follow the rules, there's a good possibility we could lose this technology."

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